Linear motor magnetic shield apparatus for lithographic systems

ABSTRACT

A magnetic shield having non-magnetic gaps provides reduced magnetic cross-talk for a linear motor array in a precision positioning system. Redirecting the leakage flux limits the cross-talk and associated deleterious effects. Such preferred magnetic circuit paths for the leakage are affixed to the moving magnet system of the linear motor. Embodiments of the preferred flux leakage paths are realized by providing a ferromagnetic shield separated by a non-magnetic gap between the permanent magnets and the back-irons. In another embodiment, the ferromagnetic shield separation includes diamagnetic materials.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. Non-Provisional application ofSer. No. 12/622,665, filed Nov. 20, 2009, which claims benefit under 35U.S.C. §119(e) to U.S. Provisional Application No. 61/141,863, filedDec. 31, 2008, which is incorporated by reference herein in itsentirety.

BACKGROUND

1. Field

Embodiments of the present invention relate to a linear motor, and inparticular to a linear motor used in precision drive applications suchas semiconductor lithography.

2. Background

Many automated manufacturing processes require the ability to move aworkpiece quickly and accurately into a location at which one or moreprocess steps are performed. In some applications, such as semiconductorlithography, such precision positioning must be achieved with anaccuracy approaching nanometers, and with speeds consistent with thethroughput requirements of modern day lithographic processes.

The challenges associated with positioning equipment to accuracies ofthe order of nanometers are significant, particularly in the context ofphotolithography systems. In the photolithography context, substratesundergo multiple processes that result in a modern day integratedcircuit. Many of these processes require that multiple steps beperformed on a substrate, where each step requires excruciatingalignment from one step to a successive step. Many of these stepsrequire the substrate to be moved into and out of one or more stages forpatterning and other operations. Not only are nanometer alignments asignificant challenge but the throughput of modern day lithographicsystems demands rapid movement to and from those precise locations.Moreover, many lithographic systems contain two or more tables such thatpreparatory steps can be accomplished in parallel with the mainprocessing steps. The use of multiple tables requires expeditiousre-positioning of the substrate in order to capitalize on the benefit ofthe multiple tables.

Linear motors have become a preferred means of positioning inlithography by virtue of their accuracy, acceleration, travel range,packaging size, improved power dissipation, reliability and longevity.In many lithographic applications, arrays of linear motors are used tomaximize the actuator force while meeting volume and other requirementsof modern lithographic equipment.

A linear motor typically includes of a magnetic circuit having permanentmagnets, a back-iron and a coil. When the coil is energized, anelectromagnetic interaction between the energized coil and the permanentmagnets generates the actuator force used for the precision positioning.

However, some amount of magnetic flux leaks out of the intended magneticcircuit of the linear motor. Because of the proximity of adjacent linearmotors, the leakage flux travels through the alternate low resistancepath offered by the permanent magnets and ferromagnetic materials withinthe adjacent linear motors. Such a path for the leakage flux results inundesirable cross-talk forces acting in conflict with the desired forcesproduced by the linear motors.

Specifically, these cross-talk forces pose the following significantconcerns to the use of a linear motor in a precision positioning system.Firstly, a fraction of the nominally available motor force is lost inovercoming cross-talk resistance in the driving direction, which resultsin increased power dissipation. Secondly, the cross-talk resistance inthe driving direction varies with the distance between adjacent linearmotors or adjacent ferromagnetic materials. Such variation posessignificant challenges to the control system of the linear motor, withpotentially unstable consequences. Finally, a cross-talk force componentin the lateral direction (i.e., lateral to the driving direction)results in undesired physical forces being applied to the frame to whichthe linear motors are mounted. The level of such forces can besignificant enough to result in deformation to the frame. For example,in a given configuration, a lateral cross-talk force of 0.1 N can resultin magnet frame deformations of the order of 20 μm. Such deformationsresult in significant challenges to linear motor design for positionsystems that already must account for packaging efficiency,manufacturing tolerances, alignment tolerances and a design safetyfactor.

Therefore, what is needed is a linear motor that can minimize the impactof magnetic leakage flux, while maintaining the benefits of accuratepositioning and rapid acceleration so necessary to meet the modernsemiconductor lithography demands.

BRIEF SUMMARY

In one embodiment of the present invention, a linear motor is providedthat reduces magnetic flux leakage by using a low reluctance shield inclose proximity, but separated from, the permanent magnets andback-irons in the magnetic circuit.

In various embodiments of the present invention, the separation of theshield is provided by air, vacuum, epoxy, diamagnetic materials, and/orhigh reluctance materials.

In further embodiments of the present invention, configurations of theshield provide varying degrees of stray magnetic flux interception andredirection.

In a further embodiment of the present invention, a multi-piece shieldincludes a shield that acts to redirect stray magnetic flux in thedirection of travel and is connected to the components of the magneticcircuit, and a shield that acts to redirect stray magnetic flux in adirection lateral to the direction of travel is stationary.

Further embodiments, features, and advantages of the invention, as wellas the structure and operation of the various embodiments of theinvention are described in detail below with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

Embodiments of the present invention are described with reference to theaccompanying drawings. In the drawings, like reference numbers indicateidentical or functionally similar elements.

FIGS. 1A and 1B respectively depict reflective and transmissivelithographic apparatuses.

FIG. 2 provides a simulation of the exemplary leakage of magnetic fluxin the magnetic circuits of two adjacent linear motors.

FIG. 3 illustrates a densely packed linear motor array configuration.

FIG. 4 illustrates a sketch of an array of three adjacent linear motorswith shields, according to an embodiment of the present invention.

FIGS. 5A and 5B respectively provide a top view and a cross-sectionalview of a linear motor with shield, in accordance with an embodiment ofthe present invention.

FIG. 6 illustrates another configuration of a shield, in accordance withan embodiment of the present invention.

FIG. 7 provides a flowchart of a method to process a substrate, inaccordance with an embodiment of the present invention.

DETAILED DESCRIPTION

While the present invention is described herein with reference toillustrative embodiments for particular applications, it should beunderstood that the invention is not limited thereto. Those skilled inthe art with access to the teachings provided herein will recognizeadditional modifications, applications, and embodiments within the scopethereof and additional fields in which the present invention would be ofsignificant utility.

FIGS. 1A and 1B schematically depict lithographic apparatus 100 andlithographic apparatus 100′, respectively. Lithographic apparatus 100and lithographic apparatus 100′ each include: an illumination system(illuminator) IL configured to condition a radiation beam B (e.g., DUVor EUV radiation); a support structure (e.g., a mask table) MTconfigured to support a patterning device (e.g., a mask, a reticle, or adynamic patterning device) MA and connected to a first positioner PMconfigured to accurately position the patterning device MA; and asubstrate table (e.g., a wafer table) WT configured to hold a substrate(e.g., a resist coated wafer) W and connected to a second positioner PWconfigured to accurately position the substrate W. Lithographicapparatuses 100 and 100′ also have a projection system PS configured toproject a pattern imparted to radiation beam B by patterning device MAonto a target portion (e.g., including one or more dies) C of thesubstrate W. In lithographic apparatus 100 patterning device MA andprojection system PS are reflective, and in lithographic apparatus 100′patterning device MA and projection system PS are transmissive.

Illumination system IL may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling the radiation B.

Support structure MT holds patterning device MA in a manner that dependson the orientation of patterning device MA, the design of lithographicapparatuses 100 and 100′, and other conditions, such as for examplewhether or not patterning device MA is held in a vacuum environment.Support structure MT may use mechanical, vacuum, electrostatic or otherclamping techniques to hold patterning device MA. Support structure MTmay be a frame or a table, for example, which may be fixed or movable,as required. Support structure MT may ensure that the patterning deviceis at a desired position, for example with respect to projection systemPS.

The term “patterning device” MA should be broadly interpreted asreferring to any device that may be used to impart radiation beam B witha pattern in its cross-section, such as to create a pattern in targetportion C of substrate W. The pattern imparted to radiation beam B maycorrespond to a particular functional layer in a device being created intarget portion C, such as an integrated circuit.

Patterning device MA may be transmissive (as in lithographic apparatus100′ of FIG. 1B) or reflective (as in lithographic apparatus 100 of FIG.1A). Examples of patterning devices MA include reticles, masks,programmable mirror arrays, and programmable LCD panels. Masks are wellknown in lithography, and include mask types such as binary, alternatingphase shift, and attenuated phase shift, as well as various hybrid masktypes. An example of a programmable mirror array employs a matrixarrangement of small mirrors, each of which may be individually tiltedso as to reflect an incoming radiation beam in different directions. Thetilted mirrors impart a pattern in radiation beam B which is reflectedby the mirror matrix.

The term “projection system” PS may encompass any type of projectionsystem, including refractive, reflective, catadioptric, magnetic,electromagnetic and electrostatic optical systems, or any combinationthereof, as appropriate for the exposure radiation being used, or forother factors, such as the use of an immersion liquid or the use of avacuum. A vacuum environment may be used for EUV or electron beamradiation since other gases may absorb too much radiation or electrons.A vacuum environment may therefore be provided to the whole beam pathwith the aid of a vacuum wall and vacuum pumps.

Lithographic apparatus 100 and/or lithographic apparatus 100′ may be ofa type having two (dual stage) or more substrate tables (and/or two ormore mask tables) WT. In such “multiple stage” machines the additionalsubstrate tables WT may be used in parallel, or preparatory steps may becarried out on one or more tables while one or more other substratetables WT are being used for exposure. When the preparatory steps can beperformed while one or more other substrate tables WT are being used forexposure, the preparatory steps are said to occur during an “in-linephase” because the preparatory steps are performed within the desiredthroughput of lithographic apparatus 100 and/or lithographic apparatus100′. In contrast, when the preparatory steps cannot be performed whileone or more other substrate tables WT are being used for exposure, thepreparatory steps are said to occur during an “off-line phase” becausethe preparatory steps cannot be performed within a desired throughput oflithographic apparatus 100 and/or lithographic apparatus 100′. Asdescribed in more detail herein, focus-positioning parameters of anexposure system (such as, for example projection system PS oflithographic apparatuses 100, 100′) may be determined in an off-linephase, an in-line phase, or a combination thereof.

Referring to FIGS. 1A and 1B, illuminator IL receives a radiation beamfrom a radiation source SO. Source SO and the lithographic apparatuses100, 100′ may be separate entities, for example when source SO is anexcimer laser. In such cases, source SO is not considered to form partof lithographic apparatuses 100 or 100′, and radiation beam B passesfrom source SO to illuminator IL with the aid of a beam delivery systemBD (FIG. 1B) including, for example, suitable directing mirrors and/or abeam expander. In other cases, source SO may be an integral part oflithographic apparatuses 100, 100′ for example when source SO is amercury lamp. Source SO and illuminator IL, together with beam deliverysystem BD, if required, may be referred to as a radiation system.

Illuminator IL may include an adjuster AD (FIG. 1B) for adjusting theangular intensity distribution of the radiation beam. Generally, atleast the outer and/or inner radial extent (commonly referred to asσ-outer and σ-inner, respectively) of the intensity distribution in apupil plane of the illuminator may be adjusted. In addition, illuminatorIL may include various other components (FIG. 1B), such as an integratorIN and a condenser CO. Illuminator IL may be used to condition radiationbeam B, to have a desired uniformity and intensity distribution in itscross section.

Referring to FIG. 1A, radiation beam B is incident on patterning device(e.g., mask) MA having a mask pattern MP, which is held on supportstructure (e.g., mask table) MT, and is patterned by patterning deviceMA. In lithographic apparatus 100, radiation beam B is reflected frompatterning device (e.g., mask) MA. After being reflected from thepatterning device (e.g., mask) MA, radiation beam B passes throughprojection system PS, which focuses radiation beam B onto target portionC of substrate W. With the aid of the second positioner PW and positionsensor IF2 (e.g., an interferometric device, linear encoder orcapacitive sensor), substrate table WT may be moved accurately, e.g. soas to position different target portions C in the path of radiation beamB. Similarly, the first positioner PM and another position sensor IF1may be used to accurately position patterning device (e.g., mask) MAwith respect to the path of radiation beam B. Patterning device (e.g.,mask) MA and substrate W may be aligned using mask alignment marks M1,M2 and substrate alignment marks P1, P2.

Referring to FIG. 1B, radiation beam B is incident on the patterningdevice (e.g., mask MA), which is held on the support structure (e.g.,mask table MT), and is patterned by the patterning device. Havingtraversed mask MA, radiation beam B passes through projection system PS,which focuses the beam onto target portion C of substrate W. With theaid of the second positioner PW and position sensor IF (e.g., aninterferometric device, linear encoder or capacitive sensor), substratetable WT can be moved accurately, e.g. so as to position differenttarget portions C in the path of radiation beam B. Similarly, the firstpositioner PM and another position sensor (which is not explicitlydepicted in FIG. 1B) can be used to accurately position mask MA withrespect to the path of radiation beam B, e.g., after mechanicalretrieval from a mask library, or during a scan.

In general, movement of mask table MT may be realized with the aid of along-stroke module (coarse positioning) and a short-stroke module (finepositioning), which form part of the first positioner PM. Similarly,movement of substrate table WT may be realized using a long-strokemodule and a short-stroke module, which form part of the secondpositioner PW. In the case of a stepper (as opposed to a scanner) masktable MT may be connected to a short-stroke actuator only, or may befixed. Mask MA and substrate W may be aligned using mask alignment marksM1, M2 and substrate alignment marks P1, P2. Although the substratealignment marks as illustrated occupy dedicated target portions, theymay be located in spaces between target portions (known as scribe-lanealignment marks). Similarly, in situations in which more than one die isprovided on mask MA, the mask alignment marks may be located between thedies.

Lithographic apparatuses 100 and 100′ may be used in at least one of thefollowing modes.

In step mode, support structure (e.g., mask table) MT and substratetable WT are kept essentially stationary, while an entire patternimparted to radiation beam B is projected onto target portion C at onetime (i.e., a single static exposure). Substrate table WT is thenshifted in the X and/or Y direction so that a different target portion Cmay be exposed.

In scan mode, support structure (e.g., mask table) MT and substratetable WT are scanned synchronously while a pattern imparted to radiationbeam B is projected onto target portion C (i.e., a single dynamicexposure). The velocity and direction of substrate table WT relative tosupport structure (e.g., mask table) MT may be determined by the(de-)magnification and image reversal characteristics of projectionsystem PS.

In another mode, support structure (e.g., mask table) MT is keptsubstantially stationary holding a programmable patterning device, andsubstrate table WT is moved or scanned while a pattern imparted toradiation beam B is projected onto target portion C. A pulsed radiationsource SO may be employed and the programmable patterning device isupdated as required after each movement of substrate table WT or inbetween successive radiation pulses during a scan. This mode ofoperation may be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable mirror array of atype as referred to herein.

Combinations and/or variations on the described modes of use or entirelydifferent modes of use may also be employed.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion,” respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.,having a wavelength of or about 365, 248, 193, 157 or 126 nm) or extremeultraviolet radiation (e.g., having a wavelength of 5 nm or above).

The term “lens,” where the context allows, may refer to any one orcombination of various types of optical components, including refractiveand reflective optical components.

FIG. 2 provides a simulation of exemplary leakage of magnetic flux inthe magnetic circuits of two adjacent linear motors 210 a and 210 b. Innormal operation, the coil (not shown) in linear motor 210 a isenergized by current. The current in the coils interacts with themagnetic flux generated by the permanent magnets, which flows in theintended magnetic circuit 230 a. The electrical current in the coil andthe magnetic flux interact to generate a force perpendicular to both.This force, known as the Lorentz force, is proportional to the currentin the coil. Notice that to a first order, the intensity of the magneticflux, and therefore the cross-talk, is independent of the coil current.However, leakage flux 240 is flux that originates in intended magneticcircuit 230 a, but closes via a portion of the adjacent magnetic circuit230 b of adjacent linear motor 210 b. Such leakage flux 240 contributesto loss of motor force and increased power dissipation in linear motors210 a and 210 b. Leakage flux 240 results in cross-talk forces with twocomponents. A cross-talk force component in the driving direction of alinear motor poses a challenge to the stability of the control systemfor the linear motor, since such a cross-talk force component varieswith distance between adjacent linear motors or adjacent ferromagneticmaterials. A cross-talk force component in the lateral direction of alinear motor poses a risk of potential deformation of the frame to whichthe linear motor is mounted.

FIG. 3 illustrates the dilemma of proximity in a densely packed linearmotor array configuration 300 that is commonly used in many precisionpositioning applications. Linear motor array configuration 300 shows atotal of 28 linear motors arrayed in a 5, 5, 4, 5, 5, 4 configuration.Such close proximity as shown in FIG. 3 results in significantcross-talk forces that need to be addressed in order to provide a linearmotor that addresses the challenges presented by modern daysemiconductor lithography and comparable precision positioningapplications. Note that the configuration shown in FIG. 3 is provided byway of example, and not by way of limitation. Those of ordinary skill inthe relevant art(s) will recognize the wide variety of configurations oflinear motors that fall within the scope of the teachings providedherein. Such configurations include but are not limited to rectangular,circular, oval, star, and octagonal arrays of linear motors.

In various embodiments of the present invention, a shield is used toreduce the flux leakage problem described above. FIG. 4 illustrates anarray 400 of three adjacent linear motors, 410 a, 410 b, and 410 c, inaccordance with an embodiment of the present invention. Only thesymmetric upper half of each of these linear motors is shown. Not shownis an identical lower half of each of these linear motors. Components oflinear motor 410 a include a coil 420 a, and a magnetic assemblyincluding two shields 430 a and 430 b, a back iron 440 a, and twopermanent magnets 450 a and 450 b. Similar components exist for theother two linear motors 410 b and 410 c. The simplified illustration inFIG. 4 shows coils 420 to be planar coils that are sandwiched betweenmirror-image magnetic assemblies, namely an upper magnetic assembly(shown) and a lower magnetic assembly (not shown). Shields 430 areportrayed as simple blocks, although the shape of the shields may be anyshape or configuration that is consistent with the requirementsdescribed below. In particular, shields 430 a and 430 b may each containmulti-piece blocks that form a desired shape or configuration.

Back irons 440 are made of ferromagnetic material, and are magneticallycoupled to permanent magnets 450 a, 450 b to complete a magnetic fluxcircuit. Permanent magnets 450 a, 450 b of the linear motor includemagnetized poles that are arranged in alternating polarity in thedirection of travel of the linear motor. Between the upper symmetrichalf and lower symmetric half of the linear motors is a gap across whichthe magnetic flux crosses, and in which coil 420 is placed. The coilincludes wire wound into a coil. In an embodiment of the coil, it can bea planar coil, a coil plate, a member of a group of separated individualcoils (that may be coplanar with each other or located in differentplanes), or any other shape or configuration consistent with thephysical space requirement. The coil can be of any thickness to meetother design requirements. For example, thicker coils typically lead toincreased motor constants, but typically require a greater separationbetween the upper and lower motor portions. The greater the separation,the higher the risk of increased flux leakage. Note that the magneticconfiguration shown in FIG. 4 is provided by way of example, and not byway of limitation. Specifically, other magnetic configurations fallwithin the scope of the teachings provided herein, including the use ofHalbach arrays, the replacement of back iron 440 with a magnet, andrearranging the magnetic flux circuit by substituting back iron 440 witha permanent magnet and permanent magnet 450 with a back iron.

FIGS. 5A and 5B provide a top view and a cross-sectional view of alinear motor 500 respectively, in accordance with an embodiment of thepresent invention. Linear motor 500 includes a coil 510, located betweentwo pairs of permanent magnets 520 a, 520 b and 520 c, 520 d. The twopairs of permanent magnets 520 a, 520 b, 520 c, 520 d are of alternatingpolarity. When energized, coil 510 has current flowing in the currentpath 530. A pair of back irons 540 a, 540 b are placed in contact withpermanent magnets 520 a, 520 b, 520 c, 520 d to complete a magneticcircuit 550. Surrounding the permanent magnets 520 a, 520 b, 520 c, 520d is a configuration of shields 560 a, 560 b, 560 c, 560 d. In anembodiment, linear motor 500 is a moving magnet design, in thatpermanent magnets 520 a, 520 b, 520 c, 520 d and back irons 540 a, 540 bmove when coil 510 is energized, while coil 510 remains stationary.

Linear motor 500 also includes a magnetic shield 560. Its purpose is tominimize the leakage flux that flows out of the intended magneticcircuit and into one or more adjacent magnetic circuits. To be aneffective shield, shield 560 should not interfere with the intendedmagnetic circuit. Rather, its focus is to redirect stray leakage fluxaway from adjacent linear motors. Based on these two objectives,redirection of the stray leakage flux may be achieved by making shield560 from a low reluctance medium in the vicinity of the stray magneticflux so as to redirect the stray magnetic flux away from the adjacentlinear motors. Avoiding interference with the intended magnetic circuitcan be achieved by ensuring a high reluctance medium exists between theintended magnetic circuit and shield 560. Accordingly, satisfactoryreduction in the leakage flux can be achieved with an open shield, andthus does not require a complete Faraday shield. Note that a completeFaraday shield can be used, if needed due to stray flux paths. However,in reality, a Faraday shield can pose significant design challenges dueto its additional weight and volume requirements. The followingdescription provides a discussion of various aspects of shield 560. Sucha discussion provides information by way of example, and not by way oflimitation.

As noted above, shield 560 provides a low reluctance path for the strayleakage flux lines. Ferromagnetic materials exhibit low reluctancemagnetic properties and are therefore suitable candidates for thematerial used in the manufacture of shield 560. Typical ferromagneticmaterials include, but are not limited to, iron, cast iron, cast steel,magnetic stainless steel, carbon steel, and iron-nickel alloys. Personsskilled in the art will recognize that in various embodiments of thepresent invention shield 560 can include other materials such that theoverall reluctance is lower than the “unshielded” path used by the straymagnetic flux.

Also, as noted above, shield 560 is separated from the intended magneticcircuit by a high reluctance medium. Such a separation is maintainedbetween the shield and the permanent magnets, as well as between theshield and the back-irons. Suitable high reluctance media include, butare not limited to, air, vacuum, and any non-magnetic material. Forexample, in FIG. 5A/5B, shields 560 a, 560 b, 560 c and 560 d areseparated from both permanent magnets 520 a, 520 b, 520 c, 520 d andback irons 540 a, 540 b by air gaps 570 a, 570 b, 570 c, 570 d.Non-magnetic epoxy, or any similar adhesive, can also be used to providethe high reluctance medium while maintaining the necessary physicalseparation.

Another alternative material capable of providing such a separation is adiamagnetic material. Diamagnetic materials present a greater reluctancethan air for the stray magnetic flux lines to pass through. Diamagneticmaterials possess a relative permeability that is less than 1, and areconsequently deemed to “repel” magnetic flux. Present day diamagneticmaterials such as Bismuth are characterized by a relative permeabilityof approximately 0.9998. However, future diamagnetic materials areexpected to provide relative permeabilities that are less than 0.9, andwould be additional candidates for providing the separation.

A particular thickness of the separation is not a requirement, but athin separation often serves to reduce the volume and mass of theshield, while intercepting as many of the stray magnetic flux lines aspossible.

Shield 560 may have a variety of different configurations. The shape ofshield 560 is driven by the need to intercept as many stray magneticflux lines as deemed appropriate to reduce stray magnetic flux problemsto a desired level. Shield 560 is shaped so as to intercept these straymagnetic flux lines and redirect, as much as possible, the straymagnetic flux lines back towards the intended magnetic circuit. In anembodiment of the present invention illustrated in FIG. 5A/5B shield 560is realized by an end-cap configuration. In such a configuration, anend-cap is placed at each end of the magnetic assembly in the traveldirection of the linear motor. Simulations for such a configurationreveal that the use of these types of shields can reduce the cross-talkforces in the driving direction by approximately 68%, and can reduce thecross-talk forces in the lateral direction by approximately 80%. A minorreduction in the motor constant of approximately 1.8% may result fromthe use of this type of shield configuration in a particular embodimentof the present invention. Note that the values presented above areprovided by way of example, and not by way of limitation. Those of skillin the relevant art(s) will recognize that a wide variety of designchoices fall within the scope of the teachings provided herein.

FIG. 6 illustrates an exemplary linear motor 600 with anotherconfiguration of shield 620, in accordance with an embodiment of thepresent invention. In the lower magnetic assembly, shield 620 a is shownwrapped around permanent magnets 610 a, 610 b, but separated frompermanent magnets 610 a, 610 b by a suitable distance. Shield 620 a isalso separated from back-iron 640 a by an epoxy 630 a. A mirror-imageupper magnetic assembly is also illustrated in FIG. 6. The uppermagnetic assembly includes shield 620 b wrapped around, but separatedfrom, a pair of permanent magnets (not shown). Shield 620 b is alsoseparated from back-iron 640 b by an epoxy 630 b.

In both of the above configurations in FIGS. 5A/5B and 6, shields 560and 620 are attached to the back-iron directly (or indirectly via amoving frame) so that shields 560 and 620 move along with the permanentmagnets. In the configuration illustrated in FIG. 6, shield 620 includesa one-piece component for each half of the magnetic assembly. Moregenerally, shield 620 can include a multi-piece construction (e.g.,laminated construction) consistent with the above requirements.

In a further embodiment, the shield can include a two-part configurationfor each of the upper magnetic circuit and the lower magnetic circuit,where one of the parts provides shielding in the lateral direction andthe other part provides shielding in the travel direction. In anembodiment, the shields for the travel direction are attached to theback iron assembly in order to maintain the shielding effect duringtravel, while the shields in the lateral direction are not required todo so.

FIG. 7 provides a flowchart of an exemplary method 700 for processing asubstrate using a linear motor with a shield to reduce flux leakage,according to an embodiment of the invention.

The process begins at step 710. In step 710, a substrate is provided.The substrate may be provided, for example, by substrate table WT, asillustrated in FIGS. 1A and 1B.

In step 720, a beam of radiation is provided. The beam of radiation maybe provided, for example, by radiation source SO, as illustrated inFIGS. 1A and 1B.

In step 730, a desired pattern is imparted onto the beam of radiation.The desired pattern may be imparted onto the beam of radiation by, forexample, patterning device MA, as illustrated in FIGS. 1A and 1B.

In step 740, the patterned beam of radiation is projected onto a targetportion of the substrate. The patterned beam of radiation may beprojected, for example, onto target portion C of substrate W, asillustrated in FIGS. 1A and 1B.

In step 750, at least one of the substrate and the patterning device isdisplaced by using a linear motor including a first and second backiron, a first plurality and a second plurality of magnetized poles, acoil within a gap formed by opposing magnetized poles, and a first andsecond open shield magnetically separated but physically proximate tothe first and second plurality of magnetized poles and first and secondback irons.

At step 760, method 700 ends.

Those skilled in the relevant art(s) will recognize that embodiments ofthe present invention are not limited to positioning of the substratevia substrate table WT and positioning of patterning device MA.Embodiments of the present invention further include, but are notlimited to, positioning illuminator IL, components within illuminator ILsuch as adjuster AD and blocking members or attenuating members (alsoreferred to as fingers) used to condition the illuminated beam ofradiation, and optical elements (such as lenses and mirrors).

It is to be appreciated that the Detailed Description section, and notthe Summary and Abstract sections, is intended to be used to interpretthe claims. The Summary and Abstract sections may set forth one or morebut not all exemplary embodiments of the present invention ascontemplated by the inventor(s), and thus, are not intended to limit thepresent invention and the appended claims in any way.

Embodiments of the present invention have been described above with theaid of functional building blocks illustrating the implementation ofspecified functions and relationships thereof. The boundaries of thesefunctional building blocks have been arbitrarily defined herein for theconvenience of the description. Alternate boundaries can be defined solong as the specified functions and relationships thereof areappropriately performed.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the invention that others can, by applyingknowledge within the skill of the art, readily modify and/or adapt forvarious applications such specific embodiments, without undueexperimentation, without departing from the general concept of thepresent invention. Therefore, such adaptations and modifications areintended to be within the meaning and range of equivalents of thedisclosed embodiments, based on the teaching and guidance presentedherein. It is to be understood that the phraseology or terminologyherein is for the purpose of description and not of limitation, suchthat the terminology or phraseology of the present specification is tobe interpreted by the skilled artisan in light of the teachings andguidance.

The breadth and scope of the present invention should not be limited byany of the above-described exemplary embodiments, but should be definedonly in accordance with the following claims and their equivalents.

What is claimed is:
 1. A device manufacturing method, comprising:projecting a patterned beam of radiation toward a substrate stage;positioning the substrate stage using a linear motor, the linear motorcomprising: a first back iron and a second back iron extending in afirst direction; a first plurality of magnetized poles arranged withalternating polarity to each other in the first direction, wherein thefirst plurality of magnetized poles are coupled to the first back iron;a second plurality of magnetized poles arranged with alternatingpolarity to each other in the first direction, wherein the secondplurality of magnetized poles are coupled to the second back iron andwherein the second plurality of magnetized poles are arranged oppositeto the first plurality of magnetized poles; a coil disposed within a gapbetween the first plurality of magnetized poles and the second pluralityof magnetized poles; a first shield comprising a first part and a secondpart detached from the first part, wherein the first shield is disposedin a first leakage flux pathway and is separated from the firstplurality of magnetized poles and the first back iron; and a secondshield comprising a third part and a fourth part detached from the thirdpart, wherein the second shield is disposed in a second leakage fluxpathway and is separated from the second plurality of magnetized polesand the second back iron, wherein the first back iron is located betweenthe first part and the second part, the second back iron is locatedbetween the third part and the fourth part, and the third and the fourthparts of the second shield are detached from the first and second partsof the first shield.
 2. The method of claim 1, wherein the coilcomprises at least one of a coil plate, a planar coil, and a member of agroup of separated individual coils.
 3. The method of claim 1, whereinthe first shield is separated from the first plurality of magnetizedpoles and from the first back iron by at least one of air, vacuum,epoxy, high reluctance material, and diamagnetic material.
 4. The methodof claim 1, wherein the second shield is separated from the secondplurality of magnetized poles and from the second back iron by at leastone of air, vacuum, epoxy, high reluctance material, and diamagneticmaterial.
 5. The method of claim 1, wherein the first and second shieldseach comprise a first and a second element, wherein the first elementsof the first and second shields are configured to provide shielding inthe first direction and have fixed positions with their respective backirons, and the second elements of the first and second shields areconfigured to provide shielding in a direction transverse to the firstdirection.
 6. The method of claim 1, wherein the first shield and thesecond shield are end-caps.
 7. A lithographic system, comprising: anillumination system configured to produce a beam of radiation; a supportdevice configured to support a patterning device that is capable ofpatterning the beam of radiation; a substrate stage configured tosupport a substrate; and a projection system configured to project apatterned beam toward the substrate stage; wherein the substrate stagehas a linear motor, the linear motor comprising: a first back iron and asecond back iron extending in a first direction; a first plurality ofmagnetized poles arranged with alternating polarity to each other in thefirst direction, wherein the first plurality of magnetized poles arecoupled to the first back iron; a second plurality of magnetized polesarranged with alternating polarity to each other in the first direction,wherein the second plurality of magnetized poles are coupled to thesecond back iron and wherein the second plurality of magnetized polesare arranged opposite to the first plurality of magnetized poles; a coildisposed within a gap between the first plurality of magnetized polesand the second plurality of magnetized poles; a first shield comprisinga first part and a second part detached from the first part, wherein thefirst shield is disposed in a first leakage flux pathway and isseparated from the first plurality of magnetized poles and the firstback iron; and a second shield comprising a third part and a fourth partdetached from the third part, wherein the second shield is disposed in asecond leakage flux pathway and is separated from the second pluralityof magnetized poles and the second back iron, wherein the first backiron is located between the first part and the second part, the secondback iron is located between the third part and the fourth part, and thethird and the fourth parts of the second shield are detached from thefirst and second parts of the first shield.
 8. The lithographic systemof claim 7, wherein the coil comprises at least one of a coil plate, aplanar coil, and a member of a group of separated individual coils. 9.The lithographic system of claim 7, wherein the first shield isseparated from the first plurality of magnetized poles and from thefirst back iron by at least one of air, vacuum, epoxy, high reluctancematerial, and diamagnetic material.
 10. The lithographic system of claim7, wherein the second shield is separated from the second plurality ofmagnetized poles and from the second back iron by at least one of air,vacuum, epoxy, high reluctance material, and diamagnetic material. 11.The lithographic system of claim 7, wherein the first and second shieldseach comprise a first and a second element, wherein the elements of thefirst and second shields are configured to provide shielding in thefirst direction and have fixed positions with their respective backirons, and the second elements of the first and second shields areconfigured to provide shielding in a direction transverse to the firstdirection.
 12. The lithographic system of claim 7, wherein the firstshield and the second shield are end-caps.
 13. A lithographic system,comprising: an illumination system configured to produce a beam ofradiation; a support device configured to support a patterning device; asubstrate stage configured to support a substrate; and a projectionsystem configured to project a patterned beam toward the substratestage; wherein the support device has a linear motor, the linear motorcomprising: a first back iron and a second back iron extending in afirst direction; a first plurality of magnetized poles arranged withalternating polarity to each other in the first direction, wherein thefirst plurality of magnetized poles are coupled to the first back iron;a second plurality of magnetized poles arranged with alternatingpolarity to each other in the first direction, wherein the secondplurality of magnetized poles are coupled to the second back iron andwherein the second plurality of magnetized poles are arranged oppositeto the first plurality of magnetized poles; a coil disposed within a gapbetween the first plurality of magnetized poles and the second pluralityof magnetized poles; a first shield comprising a first part and a secondpart detached from the first part, wherein the first shield is disposedin a first leakage flux pathway and is separated from the firstplurality of magnetized poles and the first back iron; and a secondshield comprising a third part and a fourth part detached from the thirdpart, wherein the second shield is disposed in a second leakage fluxpathway and is separated from the second plurality of magnetized polesand the second back iron, wherein the first back iron is located betweenthe first part and the second part, the second back iron is locatedbetween the third part and the fourth part, and the third and the fourthparts of the second shield are detached from the first and second partsof the first shield.
 14. The lithographic system of claim 13, whereinthe coil comprises at least one of a coil plate, a planar coil, and amember of a group of separated individual coils.
 15. The lithographicsystem of claim 13, wherein the first shield is separated from the firstplurality of magnetized poles and from the first back iron by at leastone of air, vacuum, epoxy, high reluctance material, and diamagneticmaterial.
 16. The lithographic system of claim 13, wherein the secondshield is separated from the second plurality of magnetized poles andfrom the second back iron by at least one of air, vacuum, epoxy, highreluctance material, and diamagnetic material.
 17. The lithographicsystem of claim 13, wherein the first and second shields each comprise afirst and a second element, wherein the first elements of the first andsecond shields are configured to provide shielding in the firstdirection and have fixed positions with their respective back irons, andthe second elements of the first and second shields are configured toprovide shielding in a direction transverse to the first direction. 18.The lithographic system of claim 13, wherein the first shield and thesecond shield are end-caps.
 19. A lithographic system, comprising: anillumination system configured to produce a beam of radiation; a supportdevice configured to support a patterning device that is capable ofpatterning the beam of radiation; a substrate stage configured tosupport a substrate; and a projection system configured to project apatterned beam toward the substrate stage; wherein the support deviceand the substrate stage each has a linear motor, each linear motorcomprising: a first back iron and a second back iron extending in afirst direction; a first plurality of magnetized poles arranged withalternating polarity to each other in the first direction, wherein thefirst plurality of magnetized poles are coupled to the first back iron;a second plurality of magnetized poles arranged with alternatingpolarity to each other in the first direction, wherein the secondplurality of magnetized poles are coupled to the second back iron andwherein the second plurality of magnetized poles are arranged oppositeto the first plurality of magnetized poles; a coil disposed within a gapbetween the first plurality of magnetized poles and the second pluralityof magnetized poles; a first shield comprising a first part and a secondpart detached from the first part, wherein the first shield is disposedin a first leakage flux pathway and is separated from the firstplurality of magnetized poles and the first back iron; and a secondshield comprising a third part and a fourth part detached from the thirdpart, wherein the second shield is disposed in a second leakage fluxpathway and is separated from the second plurality of magnetized polesand the second back iron, wherein the first back iron is located betweenthe first part and the second part, the second back iron is locatedbetween the third part and the fourth part, and the third and the fourthparts of the second shield are detached from the first and second partsof the first shield.
 20. The lithographic system of claim 19, whereinthe coil comprises at least one of a coil plate, a planar coil, and amember of a group of separated individual coils.
 21. The lithographicsystem of claim 19, wherein the second shield is separated from thesecond plurality of magnetized poles and from the second back iron by atleast one of air, vacuum, epoxy, high reluctance material, anddiamagnetic material.
 22. The lithographic system of claim 19, whereinthe second shield is separated from the second plurality of magnetizedpoles and from the second back iron by at least one of air, vacuum,epoxy, high reluctance material, and diamagnetic material.
 23. Thelithographic system of claim 19, wherein the first and second shieldseach comprise a first and a second element, wherein the first elementsof the first and second shields are configured to provide shielding inthe first direction have fixed positions with their respective backirons, and the second elements of the first and second shields areconfigured to provide shielding in a direction transverse to the firstdirection.
 24. The lithographic system of claim 19, wherein the firstshield and the second shield are end-caps.